/Engine/Source/Runtime/Experimental/Chaos/Public/Chaos/Island/IslandManager.h
A set of connected constraints and particles. A dynamic particle can only be in one island, and each island explicitly holds an array of its dynamic particles. Kinematic particles may be in multiple islands and we do not hold the set of these. To find kinematic particles used by an island you would need to visit all the constraints.
class FPBDIsland